1. Field of the Invention
The present invention relates to a substrate processing apparatus, and, more particularly, to a substrate processing apparatus used for film deposition processes in semiconductor fabrication, such as sputtering, chemical vapor deposition (CVD) and plasma enhanced CVD (PECVD), as well as pre-treatment processes such as substrate heating and soft etching for cleaning substrate surfaces.
2. Description of the Related Art
The integration of an integrated circuit of a semiconductor device has been now developed. Accurate reproducibility in processing from substrate to substrate and uniformity of processing within a substrate are important factors for improving productivity of highly-integrated circuits. Precise process control in various processes of substrate processing is required for achieving good reproducibility and high uniformity. More particularly, control of the substrate temperature is important for reproducibility and uniformity. For example, in an Al (aluminum) film deposition process employing a sputtering method, processing for filling fine holes with Al is performed at a temperature within the range of 400 to 500.degree. C. In order to fill the fine holes with Al without voids, it is important to precisely set the substrate temperature and uniformly control the temperature within a substrate. In deposition of W and TiN films on a substrate by the CVD process, processing is performed within a temperature range of 300 to 600.degree. C. Temperature control is an important factor in determining electrical characteristics of the W and TiN films and the film thickness distribution (the uniformity of film thickness) within a substrate. For a substrate having an increased diameter, for example, a 300 mm diameter, uniformity of the substrate temperature is more important for maintaining and improving yield.
A CVD apparatus as an example of conventional substrate processing apparatus is described with reference to FIG. 4. A structure similar to the structure of this conventional apparatus is disclosed in U.S. Pat. Nos. 5,230,741 and 5,374,594 (Nouvellus Lam Research Patent).
In FIG. 4, the inside of a reactor 111 is evacuated by an exhaust unit 112 and an exhaust mechanism 113, and maintained in a necessary reduced pressure state. A substrate 114 is clamped on a support member 115. The support member 115 contains a block heater 116 for holding the substrate 114 thereon so that the substrate 114 is heated to a desired temperature by the block heater 116. The block heater 116 comprises a sheathed heater 117 provided therein, which is connected to a heating control mechanism 118. On the other hand, the temperature of the block heater 116 is measured by a thermocouple 119 fixed on the surface of the block heater 116 by screws. The measurement data of the thermocouple 119 is input to the heating control mechanism 118. The temperature of the block heater 116 is controlled through the heating control mechanism 118 and the sheathed heater 117. The reactor 111 comprises a water-cooling passage 120 for suppressing a temperature rise by cooling water which flows therethrough.
Source gases are introduced into the reactor 111 through an upper gas introduction mechanism 121. CVD reaction of the source gases takes place to deposit a desired thin film on the substrate 114. The support member 115 comprises a mechanism for introducing a purge gas into a peripheral portion of the back of the substrate 114 so as to prevent film deposition on the back of the substrate 114 during film deposition. The purge gas is supplied from a purge gas supply mechanism 123. Unreacted gases, by-product gases and the purge gas are exhausted to the outside through the exhaust unit 112.
The substrate 114 is clamped on the support member 115 by a differential pressure chuck. The differential pressure chuck is achieved by the pressure difference produced between the internal pressure of the reactor 111 and the pressure on the back side of the substrate 114 during film deposition. The pressure difference is produced by exhausting air in an annular groove 126 and radial grooves 127, which are formed in the surface of the block heater 116 on which the substrate 114 is held. The air in the annular groove 126 and the radial grooves 127 is exhausted through an exhaust port 125 which is connected to a differential pressure chuck exhaust mechanism 124.
The block heater 116 comprises two plates having different thicknesses, i.e., an upper member 128 and a lower member 129. A groove is formed in at least one of the faying surfaces of the upper and lower members 128 and 129. The sheathed heater 117 is fixed to this groove. Since the upper and lower members 128 and 129 are joined by welding the contact portions in the outer and inner peripheral portions of the groove, the sheathed heater 117 is isolated from the atmosphere in the reactor 111 so as not to be exposed to reactive gases, such as the source gases. FIG. 4 shows a weld portion 130. The upper and lower members 128 and 129 can also be joined by other than welding such as by brazing or a method comprising providing a sealing material between the upper and lower members and screwing these members.
The purge gas supplied from the external purge gas supply mechanism 123 is passed through a purge gas inlet 135, a support member 136, a through passage 131 and a groove 132, and blown into the reactor 111 from the periphery of the back of the substrate 114. The blowoff of the purge gas from the back of the substrate 114 prevents adhesion of a deposit to the back of the substrate 114. The upper member 128 which constitutes the block heater 116 comprises the horizontal through passage 131 which is radially provided therein, and the vertical annular groove 132. The through passage 131 and the groove 132 are formed in the upper member 128 before the upper and lower members 128 and 129 are joined. The ends of the horizontal through passage 131 are provided with a cover 133 and sealed by a weld portion 134 so as to prevent leakage of the purge gas to the outside.
Another purge gas supplied from the purge gas supply mechanism 123 is passed through another purge gas inlet 137, the space between the block heater 116 and the bottom wall of the reactor 111, and the space between the block heater 116 and a shield 138, and blown into the reactor 111. This blowoff of the other purge gas prevents the source gases from entering the periphery of the block heater 116, thereby preventing adhesion of a deposit to the periphery of the block heater 116.
The above-mentioned conventional apparatus has the following problems. Although the sheathed heater 117 is fixed in the block heater 116 by welding the upper and lower members 128 and 129, welding easily causes thermal stress. To relax the thermal stress, heat treatment and secondary cutting must be performed after welding. This thermal stress is significantly increased as the diameter of the substrate 114 is increased, and brings about an important problem of making it difficult to obtain a uniform substrate temperature. Since the inside of the groove is not joined by welding the faying surfaces of the upper and lower members 128 and 129, spaces occur between the sheathed heater 117 and the upper and lower members 128 and 129. This causes a problem of a deterioration in the efficiency of heat transfer.
When the upper and lower members 128 and 129 are joined with a brazing material, the brazing material is exposed to the inner space of the reactor 111. This causes the problem of the brazing material evaporating and deteriorating due to the reactive gases during film deposition. As with welding, spaces occur between the sheathed heater 117 and the upper and lower members, thereby causing the same problem as described above.
When the upper and lower members 128 and 129 are joined by screwing, a problem occurs in that the screws become loosened due to temperature changes. The loosening of the screws causes the problem of easily deteriorating the sealing properties between the insides of the upper and lower members 128 and 129 and the atmosphere in the reactor 111.
Further, since the through passage 131 of the upper member 128 must be sealed by the cover 133 using welding or brazing after the through passage 131 is formed in the upper member 128 for supplying the purge gas, problems with heat stress and evaporation of the brazing material occur.